Method of producing tapered plates



United States Patent US. Cl. 29527.7 3 Claims ABSTRACT OF THE DISCLOSURE A method of producing tapered metal plates is disclosed which involves first pressure casting tapered metal slabs. The slabs are arranged in packs with the thicker end of one adjacent the thinner end of another, and a separating compound is interposed between mating slab surfaces. After hot rolling to form tapered plates, the plates are separated.

This invention relates to a method for producing tapered metal plates. More particularly, the invention concerns a method of producing tapered plates by hot rolling an assembly of separable, pressure-cast, tapered slabs.

There is presently considerable interest in tapered metal plates, such as titanium, titanium alloy and carbon steel plates, for fabrication of pressure vessels, aircraft components, etc. In particular, tapered plates are well suited for the fabrication of liquid storage tanks and similar vessels. In the past, tapered plates have been considered uneconomical and noncompetitive with conven tional nontapered plates; however, by the present invention, tapered plates may be produced in an ecnomical manner and may be made competitive with conventional nontapered plates.

In accordance with the invention, there is provided a method for producing tapered metal plates which comprises pressure casting metal into the form of tapered slabs, interposing a separating compound between slabs and disposing the slabs such that the thick end of one slab is adjacent the thin end of a second tapered slab, temporarily securing the slabs into a unit assembly, heating the assembly, and hot rolling to reduce the slabs to plate thickness and thereafter separating the tapered plates so produced.

It is important in accordance with the invention to utilize tapered slabs produced by pressure casting. Normal hot top casting practices produce a piping which cannot be tolerated since the piping will be exposed upon removal of the metal in the hot top and will oxidize during heating of the slab to rolling temperature. Oxides present would be rolled into the final product and result in internal defects. To avoid these problems, it would be necessary to crop the ingot below the piping; however, this reduces the yield to such an extent that the practice becomes uneconomical. Moreover, the cropping operation itself adds considerably to production costs. With pressure casting, surface conditioning of the ingot slab is not required.

In the practice of the preferred embodiment of the invention, tapered steel slabs are produced by providing a mold having an interior of the taper required in the slab and a ceramic riser at the end through which the molten metal is introduced. The mold is filled with metal from a pressurized ladle connected to the mold. In opera- 'ice tion, the ladle filled with molten metal is placed in a pressure vessel. The pressure vessel is covered with a lid in which has been inserted a pouring tube that extends into the molten steel almost to the bottom of the ladle. This gooseneck connects the pouring tube to the mold in the casting position. When air pressure is applied to the pressure vessel, the air in the molten steel causes it to rise in the pouring tube and gooseneck and enter the mold. The vertical rise of the molten metal is determined by the increase in air pressure. The casting rate may be controlled by regulating the pressurizing equipment to increase air pressure in desired increments.

Each mold may be enclosed in a flask equipped with a gate that retains the molten metal in the mold after the cast is completed. Graphite molds may be used and an insulating ceramic riser can be installed in the mold flask at the end opposite the inlet gate to feed metal to the shrinkage cavity and thus minimize the formation of voids. Electrical circuits may be used to automatically close the gate and shut off the flow of metal.

As examples of the practice of the invention, four tapered slabs of 0.15% carbon steel are produced by pressure casting in accordance with a preferred embodiment of the invention as described above. The four slabs are arranged into two packs so that the thick end of one slab is adjacent the thin end of a second tapered slab. Separating compound such as a MgO-Cr O mixture (comprising 4 parts MgO, 1 part Cr O by volume) mixed in water to form a liquid suitable for application with a paint brush is applied to the mating surfaces of the adjacent slabs in each pack. The slabs are temporarily secured by Welding to form a unit assembly. The slabs may be welded continuously around their periphery except for a breather opening at the head and tail end of each assembly.

The assemblies are heated to about 2300 F. before hot rolling. During heating and rolling of the assemblies, the welds keep the plates together and prevent slippage. Rolling schedules are advantageously selected to reduce one assembly from 7 inches thick to about 0.80 inch thick in fourteen passes (about a 9:1 total reduction) and to reduce the second assembly from 8 inches thick to about 0.80 inch thick in sixteen passes (about 10:1 total reduction). The rolling schedule employed for producing tapered plates as described above is shown in Table I.

TABLE I Rolling Schedules for Tapered Plates Samples 1 and 2 Thickness after 3 Samples 3 and 4 Pass number: Thickness after pass, in.

The thickness is measured and recorded at uniform increments of length or width along the taper of each plate. As can \be seen from Table I, a uniform reduction of thickness is achieved.

The separating compound interposed initially between adjacent tapered slabs permits the tapered plates to be separated with ease after hot rolling. Any suitable separating compound may be employed but usually a ceramic mixture as described above is the most convenient. Although reduction ratios of 10:1 are described in the aforementioned examples, it is also possible to produce and to easily separate hot rolled tapered plates of reductions of 15:1 or more. Tapered plates produced in accordance with the method described possess excellent tapered flatness.

It is apparent from the above that various changes and modifications may be made without departing from the invention. Accordingly, the scope of the invention should be limited only by the appended claims wherein What is claimed is:

'1. A method of producing tapered metal plates comprising pressure casting metal into the form of a single tapered slab, arranging two or multiples thereof of said slabs into at least one pack such that the thicker end of one slab is adjacent the thin end of another slab and with a separating compound interposed between said slabs at the mating surfaces, temporarily securing the slabs together so as to form a unit assembly, hot rolling the assembly to reduce the thickness of the tapered slabs and produce tapered plates, and disassembling the unit assembly to recover the tapered plates so produced.

2. A method according to claim 1 wherein said metal slabs are steel.

3. A method according to claim 1 wherein said metal slabs are a metal from the group consisting of commerically pure titanium and titanium alloys.

References Cited UNITED STATES PATENTS 1,926,320 9/1933 Trembour 72366 X 3,010,202 11/1961 Fromson 72-366 X 2,996,792 8/1961 Mackie 29527.7

JOHN F. CAMPBELL, Primary Examiner D. C. REILEY, Assistant Examiner U.S.Cl.X.R. 

